Analysis of pigment cell composition, pigment content, tyrosinase content and activity of three kinds of loaches, Misgurnus anguillicaudatus from Poyang Lake

Abstract Loaches, Misgurnus anguillicaudatus, from Poyang Lake are a small economic fish, falling into three categories with typical blackspot characteristics, namely, big blackspot loaches (BBL), small blackspot loaches (SBL), and non-blackspot loaches (NBL), respectively. Pigment cell composition, pigment content, tyrosinase content and activity of three kinds of loaches were investigated. Our results showed that there were three types of skin pigment cells, namely, melanophores, xanthophores and iridophores. Melanophores in dorsum were more than in abdomen. Melanophore cytosomes in BBL were larger than those in SBL and NBL, and melanosomes were the largest in stage four. The melanophores in dorsal skin of SBL or NBL were small cell bodies, spindle-like, and in chain distribution. There was an extremely significant difference in melanin content in BBL between the dorsum and abdomen (P < 0.01). There were no significant differences in melanin abdominal content, lutein and carotenoid contents among three kinds of loaches (P > 0.05). In dorsal skin, tyrosinase content was the highest in BBL, and it was significantly lower in NBL than in BBL and SBL (P < 0.01). This study reveals differences in pigment and tyrosinase content in three kinds of loaches and provides a theoretical basis for further study of the mechanism of black spot formation.